1. Field of the Invention
The present invention relates to a semiconductor memory such as a static random access memory (SRAM), a dynamic random access memory (DRAM), a read-only memory (ROM) and a programmable ROM (PROM), and memory cells used in the semiconductor memory.
2. Description of the Related Art
In recent years, with development of semiconductor integrating technology, implementation of large-capacity semiconductor memory (also referred to as only `memory`) has advanced. On the other hand, with increasing variety of demands, not only a memory having only read-only or random access function but also a memory having several kinds of functions (multi-functional memory) have been put into practice.
FIG. 4 shows a schematic arrangement of one memory cell in a memory having plural select lines e.g. A and B and their corresponding plural read lines e.g. A and B, which is one example of a conventional multi-functional memory.
In operation, when a select signal flowing in the select line A selects a memory cell 40, the data stored therein is read out into the read line A. On the other hand, when a select signal in the select line B selects the memory cell 40, the data stored therein is read out into the read line B.
If the memory is paired with plural systems of select lines and read lines as mentioned above, data of plural words can be read simultaneously. This contributes to realization of high speed memory access.
In the above known memory paired with plural systems of select lines and read lines, all select lines select memory cells arranged in row directions, and all read lines read the data stored in the memory cells in the selected row direction and transfer the data to the column direction, as disclosed, for example by Nagao et al. in JP-A-57-92483.
Now it is assumed that an operation of comparing the corresponding bits of word information stored in a semiconductor memory must be performed. In the conventional semiconductor memory, from which only the corresponding bits cannot be read out, the information must be read successively word by word and thereafter their corresponding bits may be compared with each other.
Utilizing the above described semiconductor memory paired with plural systems of select lines and read lines, data of plural words may be read out simultaneously, resulting in realization of a higher speed memory access. However, the stored data are also read out one word by one word even in this memory so that the above problem cannot be solved essentially.
In this way, the prior arts, which require the mentioned complicated procedures to perform the above operation, cannot realize a memory access of sufficiently high speed.